Delayed radiation therapy

Hello.  Jinah here.  Was wondering if anyone had a significant delay in getting radiotherapy.  I was diagnosed with TNBC in July 2012.  Had quadrantectomy.  Chemo FACx4+Tx4.  Chemo started in August 2012 and finished in January 2013.  Found out that I had an Unknown Variant in BRCA1 and BRCA2.  Genetic counsellor suggested that the BRCA2 is probably insignificant, but the BRCA1 is probably a significant mutation, considering my family history.  Mom ovarian cancer at 45 and sis bilateral breast cancer at 35.  Me breast cancer at 37.  So the idea of bilateral mastectomy was floated around.  Stupid me.  Spent too much time agonizing over radiotherapy vs. bilateral mastectomy.  Now, it is 15 weeks post last chemo.  I feel like I want radiotherapy given the possible benefits in preventing loco regional relapse in the lymph nodes and chest wall.  My tumor was quite close to the chest wall and under armpit lymph nodes.  I could always have bilateral mastectomy later should I choose to.  But I feel like, after much thought, I cannot miss this window of opportunity to kill those microscopic cancer cells hiding in the nodes...  Yet, alas, I feel like it is TOO LATE!  I know I cannot take back time, but did anyone have a similar experience?  Any one know anything about diminished efficacy of delayed radiotherapy please??  THANKS..!